[SOLVED] Question about justification (pdf)

Hi

I'd like to know something... Let's assume I'm given a function ($\displaystyle f(x_1,x_2)=\dots$). I'm then asked to prove that this function is a probability density function.

So I have to check that $\displaystyle \iint_{A \times B} f(x_1,x_2) ~dx_1dx_2=1$

Is it enough ?

And do you guys have to prove first that the function is integrable ? Or do you even prove that it's integrable ?

Thanks in advance (Bow)

These stats courses are driving me nuts (Rofl)